Signaling system



April 10, 1945.

L H. -JOHNSON SIGNALING SYSTEM Filed May 13, 1943 lul.

/NVENTOR L. H. JOH/VSN am 323mm n l QE :Fumo n QSQ 20D SEQ@ .35m

,a from/Ey ,Patented Apr. 10, 1945 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Lewis H. Johnson, Madison, N. J., 'assigner to Bell yTelephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application May 1s, 1943, Serial No. 486,811

Claims. (Cl. 17e-.18)

This invention relates to telephone systems and particularly to improvements in signaling and switching arrangements therefor whereby means are provided for reducing the signaling interval.

In telephone systems employing dials for signaling purposes it has been lcustomary to employ vthe switching operation brought about by the preceding digit has been completed, The changeover relay is capable of operating during the very first pulse of the digit., however short, and holding throughout all the intervals between pulses of the same digit, however long. Such a relay may hold from as much as .150 second following the last impulse of a digit before the release thereof signals the switching mechanism that the digit has been completed. i The "switching mechanism is therefore delayed an interval of time, before it can begin preparation for the next digit,` or before it can begin preparation for ringing the called party at the end of the last digit of a series. In a seven digit number this delay interval would occur seven times.

It is therefore anobject of this invention to reduce the time required for seizing a called 'number.

It is another object of the invention to permit an increase in the speed of dialing.

` It is a further object of the invention to eliminate the delay occasioned by the slow release change-over relay.

It is still a further object of the invention to signal the switching mechanism immediately upon termination of' a digital impulse.

With the above objects inview an embodiment of the invention discloses a system of the stepby-step type wherein current of one polarityv is employed during the pulsing period and current of another polarity is employed during the interdigltal interval, so that upon termination of each digital impulse, that is, return of the dial to normal, the change-over apparatus immediately functions to set the switching mechanism for receipt of the next digit. l l

A more complete understanding of the invention will be obtained from `the detailed description which follows and by reference' to the appended drawing which shows one embodiment thereof. l

Referring to the drawing,

Fig. 1 shows schematically an automatic telephone system of the step-by-step type having subscriber stations A and B interconnected by the usual central oflice switching mechanism including a selector S employing the present invention; y

and

Fig. 2 shows a tabular operation of the dial and principal relays involved in the circuit operation.`

The subscribersy stations -A and B are of the type customarily employed in automatic telephone systems and each station includes a dial for use in obtaining. connections with any other station. While the circuit of station A is shown in detail, that of station B is merely shown symbolically, since it is identical with that of station A. Each station is connected by a subscribers line to a central ofce containing line finder, selector, and connector switches of the well-known two motion step-by-step type.

In order to reduce the time required for seizing .a called number the subscribers stations and central oliice switching circuits are provided with rectifiers for rectifyng an alternating current and for directing the resulting currentv through proper channels during different stages of the dial operation, which will be explained hereinafter in greater detail. The pulsing and change-over relays, `which are connected in a serial loop, are poled oppositely so that normal current flows in a direction to first operate the change-over relay but not the pulsing relay. Movement of the dial from its normal position operates the pulsing relay and releases the change-over relay, the pulsing relay then responding to dial' contact openings in the usual manner. 4Upon restoration of the dial to its normal position the pulsing relay releases and the change-over relay operates immediately to condition the switching apparatus for receipt of the next digit.

y The invention will be more readily understood from a detailed description of the operation.

Assuming a call to have been originated at subscribers station A, a circuit (not shown) is closed through the switchhool: contacts thereof upon removal of handset l0 from mounting Il whereupon line finder LF seizes the line of station'A and switches it through to selector S in a normal manner, which isfamiliar to those versed in the telephone switching art. Upon station A being connected to selector S'the usual dial tone is projected over the line to the subscriber and acircuit is closed for change-over relay I2, which is energized by direct current supplied through rectiers from an. alternating current source I3.

quickly the operation of relays due to the poling of the relay windings by the various rectifiers. It is also well known that rectiers present a comparatively high resistance to current of one direction and a comparatively low resistance to current of the opposite direction. The direction of current for which the rectier Oilers a low resistance is indicated by the arrow-head. In other of alternating current source I3 to energize pulsing relay 29. This circuit can be traced from source I3 through rectifier 32, winding of relay 29, uppermostl back contact of relay I6, upper brush and terminal of line iinder LF, over line conductor II, through break contact, make-before-break contact, and impulse contact of dial I 8, lower front switchhook contact of mounting II, and back over line conductor 22, through intermediate terminal and brush of line finder LF, intermediate back contact of relay I6, upper winding of relay 29, rectifier 33, upper back conwords, positive half cycles of alternating current will flow through the rectier in the direction of the arrow while negative half cycles of alternating current will be blocked thereby. However, it is well to note in tracing circuit paths involving alternating currents and rectii'lers that negative one-half cycles of alternating current readily flow through rectiiiers having the arrow-heads pointing oppositely to the flow thereof.

The energizing circuit for change-over relay I2 may be traced from alternating current source I3, using the positive half cycle thereof, as the negative half cycle is ineffective at this instant,

through the upper winding of relay I2, rectifier I4, uppermost back contact of-relay I6, upper brush and terminal of line finder LF, over line conductor I'I, through upper back contact of dial I8, winding I9, transmitter 20, rectiiier 2|, pulsing contact (bottom back contact) of dial I8, lower front switchhook contact of mounting II, and back over line conductor 22, through intermediate terminal and brush of line iinder LF, intermediate back contact of relay I6, rectifier 23, lower winding of relay I2, upper back contact of 11th rotary step switch, and through transformer winding 24 to the grounded side of source I3. Change-over relay I2 in operating closes at its innermost front contact an energizingr circuit for relay 26 by connecting ground from innermost back contact of relay I6, through winding of re- 'lay 26 to the negative pole of grounded battery.

Relay 26, which is a slow release relay and which remains energized during the pulsing period, at its uppermost front contact prep-ares an .operating circuit for rotary magnet 21; at its intermediate front contact connects the usual holding ground to the line finder circuit LF over the lower brush and terminal thereof and energizes relay 28 in a circuit that can be traced from ground through normally closed contact of VON switch and winding of relay 28 to grounded battery; and at its innermost front contact prepares a circuit for vertical magnet 3|. Relay 2 8 operates in an obvious circuit but its operation is ineffective at this instant.

When the'calling subscriber hears the aforementioned olial tone he will proceed to wind up the dial I8 in the customary manner. It may be noted that dial I8 has the usual number of contacts comprising the off-normal contacts, which consist of a break contact at thetop and a make- Abefore-break contact thereunder, and the impulse contact at the bottom. Immediately upon movement of dial I8 from its position of rest, the make-before-break contact closes and for a very short period of time both oil-normal contacts are closed, thereby ,enabling vthe negative lhalf ,cycle tact of 11th rotary step switch, and through transformer winding 24 to the grounded side of source I3. Thus in the first step of the movement of dial I8, both the change-over relay I2 and the pulsing relay 29 are in an energized state, change-over relay I2 being energized by the positive half cycle of alternating current and pulsing relay 29 being energized by the negative half cycle of alternating current. Relay 29 in operating closes a locking circuit for relay 26, which can be traced from grounded battery through winding of relay 26, front contact of relay 29, and innermostl back contact of relay I6 to ground.

However, in the second step of the wind-up movement of dial I8 the top off-normal contact thereof opens the above-traced circuit for changeover relay I2, which releases without affecting the circuit operation.

Upon reaching the nger stop (not shown) of dial I8 the subscriber releases the dial, which then starts to return to its normal position and in doing so opens the impulse contactI thereof intermittently, thereby releasing and reoperating pulsing relay 29 a number of times corresponding to the number pulled on the dial, as is well known in the art. During each .release of relay 29 vertical magnet 3I is energized andl accordingly steps the switch mechanism (not shown) to a level corresponding to the number dialed. The circuit for magnet 3I can be traced from the negative pole of grounded battery through winding thereof, inner front contact of relay 26, back contact of .relay I2, and back contact of relay 29 to ground through back contact of relay I6. The VON switch is actuated immediately upon movement of the switch mechanism from its normal position and at its uppermost front contact prepares a circuit for rotary magnet 21; at its bottom front contact prepares a circuit for release magnet 3l and at its intermediate make-before-break contact combination transfers the original operating circuit for relay 28 to one that can be traced from grounded .battery through winding of relay 28, intermediate front contact of VON switch, back contact of rotary magnet, and thence in parallel, one path continuing over top front contact of relay 28 and intermediate front contact of relay 26 to ground, and-the other path continuing through winding of relay I6, lower back contact of 11th rotary step switch, and intermediate front contact of relay 26 to ground. Relay I6 cannot operate in this circuit since the winding thereof isy shortcircuited by the upper front contact of relay 28.

As dial I8 aproaches its normal position of rest the top break contact thereof closes before' the intermediate off-normal contact opens, and, as in the rst step of winding upV the dial, both offnormal contacts are closedand both relays I 2 and 29 are operated, as before, relay I2 being operated by the positive half cycle and relay 29,-by the negative y half vcycle ofv alternating current.

Change-over relay I 2 in operating at its uppermost ing circuit for vertical magnet 3|; vat lts upper iront contact prepares a circuit for rotary magnet 21; and at its inner front contact recloses the original operating circuit, previously traced, for relay 26. In the next step as the dial I8 reaches its nal point of rest, the intermediate off-normal contact thereof opens and releases pulsing relay 29, .which in turn closes an operating circuit for rotary magnet 21. This circuit can be traced V.from grounded battery through Winding of rotary magnet 21, inner front contactof relay 28, uppermost front contact of VON switch, upper front contact of relay I2, .back contact of relay 29, and back contact of relay `I6 to ground. It is thus .to be noted that the change-over relay I2 is operatively effective immediately upon return of dial I8 to its normal position, thereby eliminating the delaying feature required in the change-over relays of the previous systems and consequently providing a reduction in the signaling` interval.

Rotary magnet 21 in operating opens, at the back contact thereof, the alternate operating cir- -cuit for relay 28, which in releasing opens, at its inner front contact, the above-traced circuit for rotary magnet 21. During the operation of rotary magnet 21 the switching mechanism (not shown) takes one rotary step and places sleeve brush 34 in contact with one of the multiple bank terminals 36. As is well known, if this terminal is busy, ground will be connected thereto and v:III to continue hunting for a free trunk should the subscriber start rotation of dial I8'for the second digit before seizure of a free trunk. Upon reoperation of relay .26 rotary magnet 21 operates over the previously traced circuit or over the above-mentioned' circuit, which can be traced from grounded battery through winding of `magnet 21, inner front contact of relay 28, RON contact, and thence to ground through uppermost front contact of relay` 26. The switching rmech- 4anisrn is rotated another step and assuming that an idle (ungrounded) terminal is found the relays `28 and I5 arev connected in series thereto. Relay 26, being a marginal relay, cannot operate in ,series with the winding of 'relay I6 but relay I6 .energizes, since a grounded bank terminal no longer short-circuits the winding thereof, over a circuit that can be traced from grounded battery through winding of relay 28, intermediate front contact of VON switch, back contact of magnet 21, winding of relay I6, back contact of l11th rotary step switch, to ground through inter- 4.mediate front contact of relay 26.

Relay I6 in operating, at the three upper front contacts thereof cuts through the talking and `sleeve leads to the corresponding brushes of the selector S and thence to the selector terminals seized for the free trunk; at the two upper back `contacts opens the operating circuit for changeover relay I2; at the intermediate back contact 'I ``ing circuit-for relay 26. Relay I2 in restoring, fr

at the inner front contact opens another point in the holding circuit for relay 26; at the upper front contact opens a point in the operating circuit of the now retracted rotary magnet 21; and at'the backy contact closes a point in the operating circuit for release magnet 31.. Relay'26 being of a slow to release type releases after'a sufficient interval and at the top front contact thereof opens another point in the alternate' operating circuit for rotary magnet 21; at the intermediate front contact removes holding ground from the line finder LF, but not before ground has been returned from the succeeding switching mechay nism, and opens a point in the original operating circuit for relay 28; at the inner front contact opens a point in the operating circuit for vertical magnet 3|; and at the back contact thereof closes another point in the operating circuit for release magnet 31.

Upon connection to a free trunk the talking and sleeve leads are extended in the usual manner to a succeeding switching mechanism (not shown) which places busy ground upon sleeve terminal 36, whereby a locking circuit is provided for relay I6 and a holding ground for line finder LF, the previous holding ground therefor being disconnected upon release of relay 26. This locking circuit may be traced from grounded battery through winding of relay 28, intermediate'front contact of VON switch, back contact of magnet `21,winding of relay I6, lower back contact of Ilth rotary step switch, lower front contact of relay I6, selector sleeve brush 34, and thence to ground (not shown) via selector terminal y3h.

The circuit is further extendedthrough succeeding selectors (notV shown) and connector C, which may have the above inventive features ineluded therein, to the called subscriber B in the usual manner and conversation may then take place between subscribers A and B. It may be noted in view of the use of rectifying devices, such as rectifiers 2I and 38 in the station circuit of subscriber A, that talking currents are transmitted by modulation of a steady current through transmitter 20 and 'therefore pass through the circuit path in which the rectifying device oiers a low resistance-to the steady current. As the variation in the current due to speech is small compared with the normal value of the steady current itself, the whole of the speech waves will pass the rectifying device with consequent full reproduction inthe telephone receiver.

When both subscribers have completed their conversation ,and have restored their handsets, the holding ground provided by the succeeding switches is removed from sleeve terminal 36 and as a result relay I6 restores and at its inner back -contact closes an operating circuit for switch release magnet 31. This circuit may be traced from grounded battery through winding of release magnet 31, lower front contact of VON switch, back contact of relay 26, back contact of relay I2, back contact of relay 29, and to ground through back contact of relay I6. Relay 31 in operating restores the selector switching mechanism to its normal position and when the VON switch is retracted to its normal position the lower front contact thereof opens the operating circuit for release magnet 31 which thereupon releases. The circuit is now in readiness for another call.

While this invention has been shown and described as embodying certain features in a first selector circuit of a step-by-step system merely for the purpose of illustration, it is, of course,

yunderstood that various modifications may be made in the details of the circuit and that the features thereof may be applied to the succeeding selectors and connector thereof as wellas. to many other and widely varied fields without departing from the scope of the invention as dened in the appended claims. For example, the dialing time reduction features vof this invention may be similarly applied to panel systems as well as to cross bar Systems.

What is claimed is: l

l. In a telephone system, a devicefor dialing digital impulses, automatic means adapted for connection with said device, a source of current fr operating said automatic means, and means for directing one component ofr said current source through said automatic means while impulses are being transmitted by said device whereby said automatic means is responsive, said means also eiective for directing another component of said current source through said automatic means immediately at the termination of the last impulse of a digit transmitted by said device.

2. In a telephone system, a device for dialing digital impulses, automatic means adapted 4for connection with said device, a source of current for operating said automatic means, and means for directing one component of said current source through said automatic means during the pulsing period of said dialing device whereby said automatic means is operatively responsive, said means also effective for directing another component of said current source through said automatic means immediately at the termination of the last impulse of a digit transmitted by said device whereby said automatic means is further responsive.y i

3. In a telephone system, a device for transmitting impulses according to the digits of a called number, automatic means adapted for connection with said device, a source of current for energizing said automatic means, and means associated with said device for directing current of one characteristic derived from said source operatively through said automatic means during the pulsing period of said device, said means also effective to direct current of another characteristic from said source immediately upon termination of the pulsing period for further energizing said automatic means.

4. In a telephone system, a device for transmitting impulses according to the digits of a called number, automatic means adapted for connection with said device, a source of alternatingy current for operating said automatic means, and means associated with said device for directing a half cycle of said alternating current through said automatic means during the pulsing period of said device whereby said automatic means is operatively responsive, said means also effective to direct the other half cycle of said alternating current through said automatic means immediis operatively responsive, said rectifying means also eiective to direct the other half cycle of said alternating current through said automatic means immediately at the termination of the last impulse of a digit transmitted by said dial, whereby said automatic means is immediately further responsive.

.6. In al telephone system, a station circuit, an impulsing device in said station circuit for trans'- mitting impulses according to the digits of a called numbenautomatic means adapted for connection with said impulsing device,` a source of current for controlling the operation of said automatic means, and means in said station circuit for directing current therethrough so that current of one characteristic controls the said automatic means during the pulsing period and current of a distinctive characteristic is effective immediately upon termination of the pulsing period for diiierently controlling the said automatic means. 4i7. In a telephone system, a device for trans-y mitting digital impulses, a stepping relay respon'- sive to impulse currents of one polarity transmitted by saiddevice, a change-over relay respon-'- sive to current of another polarity transmitted by said device immediately at the termination of the last impulse of al digit, automatic means' ac# tuated in response toY operation of said stepping relay, and means immediately responsive to energization of said change-over relay.

8. In a telephone system, a source of alternating current, a transmitting device adapted for dividing 'said alternating current into opposite polarities, and an automatic switch responsive to said current oi one polarity for advancement thereof in one direction and responsive to said current of opposite polarity for advancement thereof in another direction.

9. In a telephone system, a stepping relay responsive to impulse currents of one polarity, a change-over relay responsive to current of another polarity, said change-over relay being 'connected in series relationship with said stepping relay, a progressively movable switch actuated in a primary direction in response to operation of said stepping relay, and means responsive to energization of said change-over relay following operation of said stepping relay, whereby said switch is actuated in a secondary direction immediately upon cessation of said impulse currents of one polarity.

l0. In a telephone system, an automatic switch, a source of alternating current for controllingl said switch, two relays connected to said source of current, each of said relays being polarized to respond to current of a different polarity, a circuit arrangement responsive to an initial energization of one of said relays for preparing said switch for operation, said circuit arrangement thereafter responsive to the interrupted operation of the other of said relays for a stepping operation of said switch, and means responsive to a second operation of the rst one of said relays for changing over from said stepping operal tion to afurther subsequent automatic operation of said switch.

11 In a telephone system, a line, a dial for transmitting impulses according to the digits of a called number connected to one end of said line. an automatic switch capable of vertical androtarial movement' having access to the other end uof said line, said switch comprising a source of alternating current, and .a pair of serially connected oppositely poled relays interconnecting said source with said line, one of said relays vibra.-

torially operative during the transmissionof 'im-` pulsesbyv said'dial 'for drivingsaid switch in a vertical direction, and the other of said relaysl immediately operative upon termination of the last impulse of a digit for driving said switch in a rotarial direction.

12; In a telephone system, a station circuit, a' reciprocating dial in said station circuit for transmitting impulses, an automatic switch adapted for connection with said dial, a source of alternating current for controlling said switch, meansv in said station circuitfor controlling theV polarity of said alternating current, said switch comprising a pulsing relay and a change-over relay lconnected with said source, means for poling said pulsing relay to .respond to current of one characteristic while pulses are being transmitted by said dial and for poling said change-over relay to respond to current of another characteristic immediately at the termination of a digital impulse train projected by said dial, a circuit re.

sponsive to operation of said pulsing relay for actuating said switch step by step in one direction, and means responsive to operation of said changerover relay for automatically actuating said switch in another direction.

13. In a telephone system, a station circuit, a Y

dial in said station circuit for transmitting im pulses, an automatic switch capable of vertical and rotarial movement adapted for connection with said station circuit, a source of alternating vcurrent for controlling said switch, rectifying means in said station circuit for controlling the polarity of said alternating current, said switch comprising a pulsing relayand a change-over relay in series relationship with said source, means for poling said pulsing relay to respond to current of one polarity while a series of impulses pertaining to one digit is being transmitted by said dial and for poling said change-over relay to respond to current of a different polarity immediately at the termination of said series of impulsesa circuit responsive to operation of said pulsing relay for actuating said switch vertically, a second circuit responsive to operation `of said rentof one lpolarity and the other of said relays -being adapted for response to current of an opsaid rst relay for transferring from said stepping operation to a, further subsequent operationoiisaid switch immediately upon completion of said stepping operation of said switch.

16. In combination, an automatic switch, a source of alternating current for controlling said switch,ia` pair of oppositely poled relays serially connected with said source, a rectier for shunting a winding of each oi said relays, said rectifiers so disposed that each of said relays is responsive to current in a different direction, a circuit arrangement responsive to an initial enen gization of one of saidrelays for conditioning said switch preparatory to operation, said arrangement thereafter responsive to vibratory operation of the other of said relays for a stepping operation of said switch, and change-over means thereafter re sponsive to a second operation of said rst relay for switching said stepping operation to a further subsequent automatic operation of said switch.

1'7. In combination, an automatic switch, a source of alternating current for controlling said switch, a pair of relays connected with said source, a pair of windings on each of said relays, said pair of windings of one relay serially connected with a corresponding pair of windings of the other relay to said source, a rectifier shunting each winding of said pairs of windings serially interconnected, said rectiers for each of said pairs of windings being oppositely poled so that each of said relays change-over relay for actuating said switch rotarily in order to extend said subscribers station to a second switch, and means for preventing interruption to the rotarial operation of said rst switch by said second circuit in the event said dial is reoperated for a succeeding digit.

14. In a telephone system, a step-by-step selector switch, a source of positive and negative current for controlling said switch, a pair of relays connected with said source of current, one of said relays responsive to positive current and the other of said relays responsive to negative current, a circuit arrangement responsive to an initial energization of said relay responsive to positive current for preparing said switch for operation, said circuit arrangement thereafter responsive to the interrupted operation of the other of said relays for a stepping operation of said switch, and means responsive to a second operation of said rst `responsive relay for changing over from said of said relays beingy adapted for response to curis responsive to current in a different direction, one of said relays vibratorially responsive to im-V pulses for driving said switch in a primary direction, and the other of said relays immediately effective upon release of said one relay'for driving said switch in a secondary direction.

18. In a telephone system, a station circuit, a dial in said station circuit for transmitting impulses according to the digits of a called number, automatic means adapted for connection with said dial, a source of alternating current for controlling the operation of said means, said means comprising a pair of relays for interconnecting said source with said station circuit, and means in said station circuit for directing current therethrough so that upon operation of said dial current of one characteristic is effective during the pulsing period thereof while current of another characteristic is effective immediately upon termination of the last impulse of a digit and during the interdigital period, one of said relays being responsive to current of said one characteristic for operating said automatic means, and the other of said v.relays being responsive to current of the other characteristic, whereby said automatic i means is rendered effective to further operation immediately upon termination of the last impulse of a digit.

19. In a telephone system. a subscribers station circuit,l a dial in said station circuit for transmitting impulses according to the digits of a called number. an automatic switch adapted for connection with said dial, a source of alternating current for controlling the operation of said switch, said switch comprising a pair of serially connected oppositely poled relays for interconnecting said source with said station circuit, rectifying means in said station circuit for directing current therethrough so'thatupon operation of said dial current of one characteristic is eiective during the pulsing period thereof While current of another characteristic is eiiective during the interdigital period, and second rectifying means for polarizing said relays, one of said relays vibratorially operative during the pulsing period of said dial for driving said switch in one direction, and the other of said relays immediately operative upon termination of `the last impulse of a digital number for driving said switch in a different direction.

20. In a telephone system, an incoming line including means for transmitting digital impulses,

an outgoing line, a switch for interconnecting said incoming and outgoing lines, said switch comprising a source of alternating current, an impulse relay interconnecting said incoming line and saidline and being responsive to current of one polarity, a second relay interconnecting said incoming line and said source, said second relay being loperative by current of an opposite polarity, and means for polarizing said relays whereby said current of one polarity is eiective during transmission of said one digital series of impulses and said current of opposite polarity is effective during an interdigital period.

LEWIS H. JOHNSON. 

